Maternal Thyroid Function and Birth Outcomes after Iodine Supplementation in Mild-to-moderately Iodine-deficient Pregnant Women in Thailand

Abstract

Objectives: To evaluate the effects of iodine supplementation in mild-to-moderately iodine-deficient pregnant Thai women on maternal thyroid function and birth outcomes. Methods: An RCT with 200 µg KI per day was conducted among 514 mild-to-moderately iodine-deficient pregnant Thai women. Blood samples were collected at baseline (<14 weeks of gestation), and follow up samples were collected in the 2nd, and 3rd trimester and at delivery in cord blood. Free T4 (fT4), thyroglobulin (TG) and thyroid-stimulating hormone (TSH) concentration were measured. Neonatal data was obtained from hospital records. Thyroid volume of the newborns was measured using ultrasonography. Data were analyzed per protocol by linear mixed models and linear regression models. Results: Cumulative loss to follow up was 20% in the 2nd trimester, 23% in the 3rd trimester, and 28% at delivery. Median maternal fT4, TG and TSH concentration did not differ significantly between treatment groups (p>0.05). Mean birth weight was 3150±410 g in the iodine group as compared to 3088±473 g in the placebo group (p>0.05); 4.8% of infants in the iodine group were low birth weight versus 7.9% in the placebo group. There were no significant differences in median fT4, TG and TSH concentration, and mean thyroid volume of the newborns between treatment groups (p>0.05).   Conclusions: Maternal iodine supplementation normalized iodine status and resulted in lower maternal TSH concentrations during pregnancy. Further data analysis should reveal whether iodine supplementation has led to any improvement in child development in this population.